mike77

My s2 did this. I adjusted the belt so that it was not in continuous contact with the idler when at stable revs. If the idler is continually spinning fast it will whine. I set mine so that the belt only came into contact with the idler when there is a sharp change in acceleration and the belt attempts to flap which is then prevented as it contacts the idler

mytrplseven

You should be able to twist the longest run of the balance belt 180 degrees with your fingers. I know it sounds too sloppy but this is the popular method. Also the idler should clear the belt by the thickness of a credit card. Good luck.